Method and device for stacking materials in sheet form with aligned lateral edges

ABSTRACT

The invention relates to a device for stacking printed materials in sheet form, for example printed sheets, with the lateral edges of the sheets aligned. According to various aspects of the invention, methods and devices for stacking printed sheets on a stacking element are provided comprising a transport path to the stacking element comprising a first transport element and a second transport element, wherein the position of the second transport element is changeable along the transport path, at least the second transport element remaining stationary during the transport of sheets.

[0001] The invention relates to a device for stacking printed materials in sheet form, for example printed sheets, with the lateral edges of the sheets aligned.

[0002] In devices for the printing and the processing of printed materials, the printed materials are often piled on a stack. To facilitate the further processing, for example, to bind a stack of printed materials into a book or to transport bigger stacks, it is advantageous if the printed sheets form a square stack, if possible, with the lateral edges of the printed sheets in precise alignment. Typically, the stacks are therefore aligned in various ways, especially with jogging devices that jolt the stack, especially in the area of the uppermost printed sheet, in regular intervals, thus generally aligning it against a stop.

[0003] A device of this type is disclosed in U.S. Pat. No. 3,733,070, for example, where jogging devices, which always act in the upper area of the stack, are provided for all four sides of a stack. Furthermore, the continually growing stack is lowered vertically such that the upper edge of the stack retains an essentially constant height.

[0004] Another sheet stacking apparatus for printed materials stacked with the lateral edges in precise alignment is found, for example, in the unexamined European patent application EP 820 948 A2, which in particular discloses in FIG. 3 an aligning paddle 11 that presses the leading edge of a new delivered sheet against a stop by rotation.

[0005] A special embodiment of joggers is found, for example, in the German unexamined patent application DE 196 41 918 A1, where one jogger of a pair of joggers has an elastic surface, especially with elastic bristles that compensate the sheet tolerances, which are attached with a downward slant.

[0006] Digital printers and copiers often process various sheet formats. Furthermore, the printed materials in sheet form are processed in different orientations, i.e., in portrait format or in landscape format. Stacking printed materials in sheet form with the lateral edges in precise alignment is made more difficult in that generally the stops and/or the joggers have to be adapted to the respective format and the respective orientation of the printed sheet. Thus, there is a need for an improved device for stacking printed materials in sheet form with various sheet formats and orientations with the lateral edges of the sheets in precise alignment.

SUMMARY OF THE INVENTION

[0007] According to various aspects of the invention, methods and devices for stacking printed sheets on a stacking element are provided for sheets having a variable length.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 presents a schematic lateral view of the device according to one aspect of the invention.

[0009]FIG. 2 presents a schematic top view of the FIG. 1 device.

DETAILED DESCRIPTION

[0010] Various aspects of the invention are presented with reference to FIGS. 1 and 2, which are not drawn to any particular scale, and wherein like components in the numerous views are numbered alike. FIG. 1 and FIG. 2 show a schematic lateral view, and a schematic top view, respectively, of a device 100 according to one aspect of the invention. Other drives and/or guide means and cam disks, which are known to one of ordinary skill in the art and required for the operation of the device, are described only schematically or generally. Stepper motors are desirable because their movement can be controlled simply and precisely by control means known to one of ordinary skill in the art.

[0011] The device 100 in accordance with the invention is part of a printing-, copying- or processing device for processing sheets, which is known to one of ordinary skill in the art, in particular the part of said printing- or processing device for printed sheets that relates to the stacking of printed sheets. Because one of ordinary skill in the art knows from the state of the art a great number of printing- or processing devices of this type which process sheets, said printing- or processing devices for sheets are not disclosed in full in the following, in particular because their embodiment is not relevant to the present invention.

[0012] As shown by FIG. 1, a printed sheet 1, which is to be stacked with its lateral edges in precise alignment, is on a transport path 2, identified with the reference symbol 2, through a printing- or processing device that processes sheets (not shown). Along the transport path 2, the printed sheet has a length identified with the reference symbol 1′ in FIG. 2. The printed sheet 1 generally is paper with varying sheet weight or plastics foils, such as transparencies, but may also be a combination of papers and foils or a combination of papers with various base weights, for example for the cover of a book as opposed to the sides of the book body; however, the outer edges of the printed sheets collected in a stack should have essentially the same dimensions. When stacking the printed sheets 1 with their lateral edges in precise alignment onto a subsequent stack, for example after stacking a book all sides which are to be bound, the individual printed sheets 1 all will again essentially have the same dimensions. However, said essentially same dimensions of the printed sheets 1 may not correspond to the essentially same dimensions of the printed sheets 1 of the preceding stack because there may be a new sheet format or a new sheet orientation.

[0013] The printed sheets 1, which are used in a device that comprises the device in accordance with the invention and move on the transport path 2 in said device may have a different length 1′, for example if different formats of the printed sheets 1 are processed, or if the printed sheets 1 move at different alignments along the transport path 2, i.e., either in the so-called portrait format or in the landscape format. Both are found relatively frequently in particular in digital printing machines/copiers or print processing devices because such devices generally already include a number of paper supplies or may, for example, comprise devices to change the alignment of the printed sheets 1. Thus, many printers/copies may include, for example, paper bins for paper in the A3 and A4 formats as well as the A4R format.

[0014] On the transport path 2, the printed sheets 1 are first guided and transported by a first transport element 10, which is arranged above the transport path 2 and a second transport element 20, which is arranged below the transport path 2. Advantageously, the transport path 2 has a centerline M1, which coincides with the centerline M2 of the printed sheets 1 (see FIG. 2), regardless of the format of the orientation of the printed sheets 1. This type of transport is called a centerline registration of the printed sheets 1. However, the device 100 in accordance with the invention is not limited to the transport of centerline-registered printed sheets 1; the device 100 in accordance with the invention can also stack printed sheets 1 that are registered along their lateral edges with the lateral edges in precise alignment.

[0015] At least one of the two transport elements 10, 20 is driven to move the printed sheet 1 along the transport path 2. Advantageously, both transport elements 10, 20 are driven synchronously. In a preferred embodiment, the first transport element 10 is developed as a continuous transport belt 11 that runs tightly over two transport rollers 12. Alternatively, two or more transport belts 11 arranged parallel to one another are provided. A plurality of transport rollers 12 arranged above the transport path is also within the scope of the invention. The development of the first transport element 10 with a continuous transport belt 11 has the advantage that the printed sheet 1 is guided across a large contact surface over a longer path, which leads to a secure transport of the printed sheet 1 along the transport path 2. By developing the first transport element 10 as a transport belt, the transport rollers 22 of the second transport element 20 can be arranged along the transport path 2 at a plurality of various positions along the transport path 2 in contact with the transport belt 11 to ensure a steady and sufficient friction contact between the transport elements 10, 20 and a printed sheet 1 to be transported.

[0016] The second transport element 20 has a plurality of transport rollers 22 (see FIG. 2) arranged relative to the first transport element 10 in such a way that a transport path 2 for printed sheets 1 is created between the first transport element 10 and the second transport element 20. At least the last transport roller 22 arranged downstream is arranged in a bearing (not shown) that is known to one of ordinary skill in the art so as to allow a displacement of the position of said transport roller 22 along the transport path 2. An alternative embodiment may also provide for a plurality of transport rollers 22 that are arranged side-by-side in alignment relative to one another (see FIG. 2, which shows two transport rollers 22).

[0017] A flat stacking element 50 is attached below the two transport elements 10, 20. Along the transport path 2, the flat stacking element 50 has a length that corresponds at least to the length 1′ of the largest printed sheet 1 to be stacked. The flat stacking element 50 has guide and bearing elements (not shown) that are known to one of ordinary skill in the art from the state of the art, as well as drive and control means known from the state of the art, by means of which a controlled, essentially vertical movement of the flat stacking element 50 is possible. The direction of movement of the flat stacking element 50 is identified in FIG. 1 with the reference symbol 52. To facilitate the lateral removal of a stack of printed sheets 1 from the flat stacking element 50, the flat stacking element 50 advantageously has a downstream tapered flank 50′.

[0018] A control 70 (CPU), of a type known to one of ordinary skill in the art, but not shown here in detail, is provided to control the vertical position and the essentially vertical movement 52 of the flat stacking element 50, so that the upper edge of the stack has an essentially constant height during the stacking of the printed sheets 1. To that end, the flat stacking element 50 is lowered corresponding to the thickness of the stacked printed sheets 1 after each drop of a printed sheet 1. Alternatively, the control 70 may also provide that the flat stacking element 50 is supposed to be lowered only after x number of printed sheets have been dropped. The control 70 can have an allowance stored in a control logic, which contains a correlation between the thickness of the sheet and the number of the printed sheets 1 to be stacked after which the flat stacking element is to be lowered. Advantageously, the control 70 receives the information about the thickness of the printed sheets 1 from a user, an overriding control, sensors, or other sources of information. Additionally, the control 70 controls a longer, essentially vertical movement of the flat stacking element 50 to ensure a quick removal of the stack, for example. The flat stacking element 50 is limited along the transport path 2 by a stop 30 that can be pivoted around a center of rotation 31. As shown in FIG. 2, the stop is provided two-fold in symmetrical arrangement to the centerline M1 of the transport path. This arrangement is advantageous, but not absolutely necessary for the device 100 in accordance with the invention; it is within the scope of know how of one of ordinary skill in the art to attach a different number and/or arrangement of stops. The stop 30 is attached to pivot around the point of rotation 30 to ensure a lateral removal of the stack of printed sheets. Alternatively, an essentially vertical or horizontal movement is also conceivable within the scope of the invention to take the stop out of the path.

[0019] A flexible, rotatably driven aligning paddle 61 attached on a shaft 60 is attached above the flat stacking element 50, downstream of the two transport elements 10, 20. In the embodiment, the aligning paddle 61 is attached to the shaft 60 in such a way that it projects at both sides of the shaft 60 with the same length. Alternatively, it is also possible to provide a larger number of individual aligning paddles 61, especially to create a different angle division on the shaft 60. Alternatively, a plurality of identical aligning paddles 61 are attached along the shaft 60, advantageously symmetrically to the centerline M1 of the transport path 2. The aligning paddle 61 can also be developed curved in a curve line. In that case, the direction of the curve line is advantageously opposite the direction of rotation of the aligning paddle 16 around the shaft 60, which is identified with the reference symbol 62.

[0020] The aligning paddle 61 is arranged in a vertical distance from the upper edge of the stack of printed sheets 1 so that it comes into contact with the uppermost printed sheet 1 when rotating around the shaft 60 in the direction of movement 62 identified with the reference symbol 62 and, during further rotation, transports said printed sheet in the direction of transport as a result of friction between the aligning paddle 61 and the uppermost printed sheet 1 of the stack. Thus, the ideal material for the aligning paddle is in particular a rubber-like or plastics-like material, or a comparative coating of another flexible material, such as spring steel, for example.

[0021] Before a printed sheet 1 is dropped by the first and second transport element 10, 20, it is already in contact with the aligning paddle 61 and is guided along by the friction contact in a precise manner and driven against the stop 30. During further rotation, the aligning paddle 61 snaps around the shaft 60 and the opposite wing of the aligning paddle 61 can receive the next printed sheet 1.

[0022] Before the rear edge of the printed sheet 1 leaves the contact area to the first transport element 10 and the second transport element 20, the front edge of the printed sheet 1 is essentially in free flight toward the flat stacking element 50 along the flight line 3 illustrated as a dash-dot line in FIG. 1 to the point where the aligning paddle 61 comes into contact with the uppermost printed sheet 1. However, immediately before the rear edge of the printed sheet 1 leaves the contact area between the first transport element 10 and the second transport element 20, the aligning paddle 61 is not yet in contact with the stack of printed sheets 1. Rather, there is a narrow gap between the end of the aligning paddle 61 and the already aligned and stacked uppermost printed sheet 1, so that the front edge of a printed sheet 1 moving on the flight line 3 can move forward under the aligning paddle 61 until it is caught by the aligning paddle 61 during the rotation around the shaft 60. As soon as the aligning paddle 61 is in contact with the printed sheet 1, the rear edge of the printed sheet 1 leaves the contact area between the first transport element 10 and the second transport element 20.

[0023] The last transport roller 22 arranged downstream has a drive (not shown) that is known to one of ordinary skill in the art, from the state of the art, that moves the transport roller 22 along the guide and bearing elements provided for this purpose. The dimensioning of the provided guide and bearing elements of the transport roller 22 is such that a movement of the transport roller can be moved over a distance that is identified with the reference symbol 24. The length of the distance 24 is adjusted to the various lengths 1′ of the printed sheets 1 to be stacked and essentially corresponds to the difference between the shortest length 1′ of one of the printed sheets 1 to be stacked with the device 100 in accordance with the invention and the longest length 1′ of one of the printed sheets 1 to be stacked with the device 100 in accordance with the invention.

[0024] In the figures, the reference symbols of the transport roller axis 21 and the last transport roller 22 without apostrophe arranged downstream refer to the position of the transport roller axis 21 and the transport roller 22 in the configuration for the stacking of the longest printed sheet 1. The reference symbols of the transport roller 21 with apostrophe and the last transport roller 22 arranged downstream refer to the position of transport roller axis 21 and transport roller 22 in the configuration for the stacking of the shortest printed sheet 1.

[0025] A control 70, which is not shown in detail, but known to one of ordinary skill in the art, controls the position of the transport roller axis 21 of the last transport roller 22 arranged downstream in accordance with the length of the printed sheet 1 to be stacked. The control 70 receives the information about the length 1′ of the printed sheet 1 from a user, an overriding control, sensors, or other sources of information.

[0026] As shown in FIG. 2, lateral jogging devices 40 are arranged laterally to the flat stacking element 50 and can be moved by means of a movement in the direction of the arrow identified with reference symbol 42 from a non-contact position 41 into a position 41″ that is in contact with the stack and laterally jog the stack. In a preferred embodiment, the first or the second lateral jogging device 40 has elastic bristles (not shown) from the aforementioned state of the art, which elastically compensate sheet tolerances during the jogging. Said bristles are especially advantageously directed at a 45° angle against the plane of the flat stacking element 50, but other angles are also conceivable. Furthermore, in an alternative embodiment, one of the lateral jogging devices 40 can have a foam rubber-like or other type of compressible surface. The other lateral jogging device 40 is shaped with a smooth, incompressible surface.

[0027] The first and second jogging device 40 are moved toward the stack and away from the stack synchronously by a control 70, thus achieving an optimum lateral alignment of the printed sheets 1 in the stack. The synchronous movement of the lateral jogging devices 40 can be a cyclical movement, for example after x number of sheets have been stacked. Advantageously, the movement is initiated precisely after the aligning paddle 61 has driven the latest stacked printed sheet 1 against the stop 30.

[0028] Rear joggers 28 are arranged at the second transport element 20 below the transport path 2. By means of a movement of the transport roller axis 21 in combination with the transport roller 22 into the direction of transport, said rear joggers come into contact with the stack of stacked printed sheets 1 and jog said stack from the rear. The rear joggers are made of an elastic material, such as spring steel or plastic, and may be vertical paddle shape.

[0029] For the rear jogging of the stack along the direction identified with the reference symbols 25, 25′, the rear joggers 28 are brought into a position 28″ from a position 28′, where they come into contact with the rear edges of the printed sheets 1 stacked onto the stack. The jogging movement is performed each time after x number of sheets have been stacked, especially after each one. It goes without saying that other intervals, such as after each second, third or fifth printed sheets are also within the scope of the invention. The location of elements 21, 22, and 28 without the prime shown in FIG. 2 is for sheets having a larger length 1′, and may correspond to a maximum length, for example. The location of elements 21, 22, and 28 with the prime shown in FIG. 2 is for sheets having a lesser length 1′, and may correspond to a minimum length, for example. The elements 21, 22, and 28 may be attached to the same moveable structure, or may be attached to separately moveable structures.

[0030] In a particular embodiment of the device 100 in accordance with the invention, a control 70 features a logic that prevents the rear jogging under certain conditions. That is necessary when the rear edges of the printed sheets 1 have an irregular format, or when sheets with tab recesses or register sheets are involved.

[0031] In the following, an example of the sequence of stacking printed sheets 1 on a stack by means of the device 100 in accordance with one aspect of the invention is explained. A control 70 contains information about the length 1′ and the number of essentially identical printed sheets 1 that are to be stacked into a stack with precisely aligned lateral edges. In accordance with the determined length 1′, the control 70 controls the drives of the transport roller 22 for a movement along the transport path 2, so that the length 1′ of the printed sheets 1 essentially corresponds to the flight line 3 of the aligning paddle 61. Furthermore, the lateral jogging devices 40 are driven into a position 41, where they are near the lateral edge of the printed sheets 1.

[0032] Then the first printed sheet is pulled in, transported to the stacking location with the first and the second transport element 10, 20 and the front edge of the printed sheet 20 is essentially transported along the flight line 3 in the direction of the aligning paddle. The printed sheet 1 slides through the gap between the aligning paddle 61 and the flat stacking element 50 and is driven against the stop 30 by the rotation of the aligning paddle 61 around the shaft 60. Then the printed sheet 1 is aligned laterally by means of the lateral jogging devices 40, and finally jogged from the rear with the rear joggers 28.

[0033] After the first printed sheet 1 has been precisely stacked in this way, the flat stacking element 50 is lowered essentially vertically by the thickness of the printed sheet, whereupon the lateral jogging devices 40 move from the position 41″, where they are in contact with the stack, away from the stack and back into the position 41. The rear jogger 28 also moves back again and the second transport element 20 is once again in the ideal dropping position for the next printed sheet 1.

[0034] This process is repeated for all printed sheets 1 to be stacked. When the last printed sheet 1 is on the stack, the lateral jogging devices 40 are brought into the position 41″, i.e., into contact with the stack, and/or the rear joggers 28 are brought into the position 28″, i.e., into contact with the stack, to lower the flat stacking element 50 in a longer, essentially vertical movement, for example to remove the stack laterally, so as to ensure that together with the stop 30 the stack is guided on four sides during the quick lowering. In that way, the lateral jogging devices 40, which clamp the stack firmly, are moved downward as well.

[0035] Not shown, but also within the scope of the invention, are guide elements such as metal sheets or plastic adapting pieces, which are arranged along the flight line 3 and limit the same.

[0036] According to certain aspects of the invention, first and second transport elements are in active cooperation with one another and are driven such that they move a printed sheet along the transport path of the printed sheet at a specific transport speed. As long as the printed sheet is on the transport path between the first and the second transport element, it is guided with precision. As soon as the rear edge of the printed sheet leaves the contact area to the first and the second transport element, the printed sheet is essentially in free flight to the flat stacking element. Said flight path, on which the printed sheets are therefore essentially not guided, contributes to imprecision in stacking the printed materials and should therefore be as short as possible. Advantageously, the printed sheet is at no time in free flight, but instead is guided at all times. To keep the free flight path as short as possible with the various formats and/or orientations of the printed sheets, which are stacked with the lateral edges in precise alignment, the position of at least one of the transport elements, especially the second transport element, is adjusted in accordance with the invention to the format size and/or the orientation of the printed sheet by adjusting it along the transport path. Especially advantageously, the position of at least one transport element is adjusted such that the sheet is not in free flight at any time.

[0037] Advantageously, a control (CPU) may be provided that automatically controls the position of the second transport element depending on the length of the printed sheets to be stacked. In this context, the length of the printed sheet to be stacked is the expansion of the printed sheet along the transport path. The control may comprise elements to detect the length of the printed sheet to be stacked. Said elements for detecting the length of the printed sheet to be stacked may include sensors that determine the length of the printed sheet to be stacked, but can also include storage means where the length of the printed sheets are stored, such as a reference table or an overriding control such as the control of a host printing machine, which provides the information about the length of the printed sheet to be stacked to the device for the stacking of the printed sheets. The control of the position of the second transport element may use the information about the length of the printed sheet to be stacked to calculate the most favorable position for the second transport element to obtain the shortest possible free flight path. Alternatively, the respective most favorable position may also be stored in a reference table, for example regarding the various sheet formats that are to be stacked by means of the device in accordance with the invention. By means of the drives and bearings of the second transport element, the adjustment of the position of the second transport element can therefore be set automatically to the respective length of the printed sheet.

[0038] In another advantageous embodiment, the first transport element is developed as a stationary, continuous transport belt. In this way, a second transport element, which may be developed for example as a roller or a pair of rollers, can be moved along the transport path while simultaneously remaining in contact with the first transport element without changing the position of the first transport element, which has structural advantages and is more cost-effective in production. On the other hand, the first transport element may also be a pair of rollers that corresponds to the second transport element, which is displaced along the transport path together with the second transport element.

[0039] Advantageously, the flat stacking element may have a drive and a bearing, which allows an essentially vertical movement of the stacked stack of printed sheets. For example, the stack can be driven up or down to facilitate the removal of the stacked printed sheets by an operator or a device for the further processing of a stack of printed sheets, such as a device for the binding of book blocks. Bearings and drives for the essentially vertical movement of the flat stacking element are sufficiently known to one of ordinary skill in the art from the state of the art.

[0040] Advantageously, a control may be provided that controls the essentially vertical movement of the flat stacking element for stacks of printed sheets such that the upper edge of the stack essentially remains at the same height during the stacking of a plurality of printed sheets on the flat stacking element. This guarantees that the printed sheets always retain the same height to be dropped on the flat skid element, which leads to an improvement in the precision of the alignment of the lateral edges of the printed sheets.

[0041] In an advantageous embodiment according to a further aspect of the invention, a first jogger may be attached transverse to the transport path at the flat stacking element, and a second jogger may be attached opposite thereto, with the first and second joggers cooperating for the lateral alignment of the stack created after a number of printed sheets have been stacked. Advantageously, the first or the second jogger may have elastic bristles that elastically compensate the sheet tolerances during the jogging. The jogging the stacked sheets results in the alignment of the lateral edges of the printed sheets in the stack, especially if the printed sheets are not immediately deposited at the intended place on the flat stacking element.

[0042] In an advantageous embodiment according to a further aspect of the invention, the transport path of the printed sheets may end at a stop above the flat stacking element. Thus, the printed sheets fly from the first and second transport element on the transport path onto the stack on the flat stacking element and they reach a stop at the end, causing them to lie undisturbed on the stack. Alternatively, the stacking of the printed sheets on the stack on the flat stacking element can be improved with multiple stops.

[0043] By limiting the transport path by means of a stop, the printed sheets are advantageously aligned at the front edge. For example, this is advantageous if at least some of the printed sheets are sheets with at least partially irregular outer contours, such as register sheets or sheets with tab recesses. To stack such printed sheets with irregular outer contours so that at least segments of the lateral edges are in precise alignment, said printed sheets have at least one straight side that is guided to a stop for alignment and/or can be aligned retroactively with joggers, which in this case would be the front end of the printed sheet. In most cases, such register sheets or sheets with tab recesses have three shared edges.

[0044] In an advantageous embodiment according to a further aspect of the invention, the stop can be pivoted downward, thus releasing a lateral transport path for a stack of printed sheets stacked on the flat stacking element. This is an advantage if a set of printed sheets was stacked into a stack at the stop and is then supposed to be removed stack by stack laterally, for example by an operator or by a processing device such as a binding device for books. Displacing the stop in a vertical or lateral direction or moving the stop out of the lateral transport path by a non-pivoting movement is within the scope of the know-how of one of ordinary skill in the art.

[0045] In an advantageous embodiment according to a further aspect of the invention, vertical rear joggers are arranged at the second transport element below the transport path. Said rear joggers can come into contact with the stack of stacked printed sheets by means of a movement of the second transport element in the direction of the transport and jog said sheet stack from the rear. In this way, the mobility of the second transport element, which is available for the format adjustment because of the drive of the second transport element, may be used for the additional adjustment of the rear edge of the printed sheet against a stop after a printed sheet has been stacked. Advantageously, after each printed sheet has been stacked, the second transport element with the vertical rear joggers move from the drop position to the stack of printed sheets collected on the flat stacking element until the advantageously springy rear joggers come into contact with the stack and press said stack against a stop, thus aligning the rear edges of the individual printed sheets in the process. Then the device in accordance with the invention returns to its stacking position. In an alternative mode of operation of the device in accordance with the invention, the printed sheets are jogged after a specific number of printed sheets have been stacked, for example after each second, third or fifth printed sheet. It goes without saying that other intervals between the jogging movements are also conceivable.

[0046] In an especially advantageous manner, a mobile, driven aligning paddle may be attached above the flat stacking element. Said paddle drives a printed sheet to be stacked against a stop, with the aligning paddle advantageously being mounted to rotate in bearings. The advantageously springy blade of the paddle is in a vertical distance from the upper edge of the stack of printed sheets, thus making contact with the uppermost printed material in the rotation around a rigid axle and during continued rotation it continues to transport said printed sheet into the direction of transport because of the friction between the aligning paddle and the printed sheet. Thus, a suitable material for the aligning paddle would be especially a rubber- or plastic-like material, or a comparative coating of another flexible material such as spring steel. As soon as a printed sheet dropped by the first and second transport element is in contact with the aligning paddle, it is again guided in a precise manner by the friction contact.

[0047] In an especially advantageous embodiment according to an aspect of the invention, the second transport element for the transport of a printed sheet may assume a position in active relation to the first transport element, so that the distance of the second transport element to the aligning paddle is adjusted to the length of a printed sheet to be stacked in such a way that the printed sheet does not lose contact to the second transport element until it is in contact with the aligning paddle. In this way, the printed sheet is at no time in free flight, but is instead always guided securely, thus preventing at all times an uncontrolled flight path of a printed sheet from the first and second transport element to the stack, even when the formats of the printed sheets are different.

[0048] Advantageously, the second transport element may have vertical rear joggers below the transport path and the second transport element is displaceably mounted in such a way that as the flat stacking element with a stack of printed sheets is lowered, the rear joggers can be moved into a position where they can serve as the rear guide for the stack of printed sheets. In this way, it is ensured during the continued transport of the stack that the alignment of the printed sheets in the stack is retained as best as possible. This is relevant in particular because the process of the vertical displacement of the stack of printed sheets 1 on the flat stacking element has to proceed very quickly, which, in the absence of such a measure, often leads to a skidding of the precisely aligned stack due to the extreme positive and negative acceleration forces.

[0049] Although the invention was described in reference to preferred exemplary embodiments, the invention is not restricted to them, but can undergo changes and adaptations within its area of applicability. 

What is claimed is:
 1. A device for stacking printed sheets on a stacking element, comprising: a transport path to the stacking element comprising a first transport element and a second transport element, wherein the position of the second transport element is changeable along the transport path, at least the second transport element remaining stationary during transport of sheets.
 2. The device of claim 1, comprising a control that automatically controls the position of the second transport element as a function of a length of the sheets.
 3. The device of claim 1, wherein the first transport element is a stationary, continuous transport belt.
 4. The device of claim 1, wherein a position of the stacking element is changeable essentially vertically.
 5. The device of claim 4, comprising a control that controls a position of the stacking element such that an upper surface of the stack essentially remains at the same height during stacking.
 6. The device of claim 1, further comprising opposing jogging devices moveable in a direction transverse to the transport path, wherein the opposing jogging devices cooperate for lateral alignment of the sheets on the stacking element.
 7. The device of claim 1, comprising rear joggers below the transport path moveable in a direction of sheet transport to jog a rear of the stack.
 8. The device of claim 1, wherein the transport sends the sheets to a stop disposed at one end of the stacking element.
 9. The device of claim 8, wherein the stop is mounted to pivot downward, thus releasing a lateral transport path for a stack of sheets.
 10. The device of claim 8, comprising vertical rear joggers below the transport path moveable in a direction of sheet transport to jog a rear of the stack.
 11. The device of claim 8, comprising a driven aligning paddle disposed above the stacking element.
 12. A device for stacking printed sheets on a stacking element, comprising: a stop disposed at one end of the stacking element; a transport path to the stacking element comprising a first transport element and a second transport element, wherein the position of the second transport element is changeable along the transport path, at least the second transport element remaining stationary during transport of sheets, wherein the transport sends the sheets to the stop; rear joggers below the transport path moveable in a direction of sheet transport to jog a rear of the stack; and opposing jogging devices moveable in a direction transverse to the transport path, wherein the opposing jogging devices cooperate for the lateral alignment of sheets on the stacking element.
 13. A method for stacking printed sheets on a stacking element, comprising: delivering the sheets to the stacking element via a transport path comprising a first transport element and a second transport element opposite the first transport element; and, changing a position of the second transport element along the transport path, at least the second transport element remaining stationary during transport of sheets.
 14. The method of claim 13, comprising automatically controlling the position of the second transport element as a function of a length of the sheets.
 15. The method of claim 13, comprising controlling a position of the stacking element such that an upper surface of the stack essentially remains at the same height during the stacking.
 16. The method of claim 13, further comprising laterally aligning the stack with opposing jogging devices moveable in a direction transverse to the transport path.
 17. The method of claim 13, comprising jogging a rear of the stack with rear joggers below the transport path moveable in a direction of sheet transport.
 18. The method of claim 13, the transport path sending the sheets to a stop at one end of the stacking element.
 19. The method of claim 18, wherein the stop is mounted to a pivot, and comprising pivoting the stop downward thus releasing a lateral transport path for a stack of sheets.
 20. The method of 13, comprising an aligning paddle disposed above the stacking support, and comprising maintaining control of each sheet with the transport path until sheet contact with the aligning paddle has already been made. 